1. Field of the Invention
The present invention relates to a boat propulsion unit, and more specifically, to a boat propulsion unit that includes a first propeller and a second propeller.
2. Description of the Related Art
A boat propulsion device (boat propulsion unit) that includes a first propeller and a second propeller is conventionally known (see WO 2007/007707 A1, for example). WO 2007/007707 A1 discloses a boat propulsion unit including: a drive shaft; a first shaft that extends in the fore-and-aft direction perpendicular or substantially perpendicular to the drive shaft, and that is provided with a front propeller (first propeller) at the rear end; a second shaft that extends in the fore-and-aft direction perpendicular or substantially perpendicular to the drive shaft, and that is provided with a rear propeller (second propeller) at the rear end; a forward-reverse switching mechanism that is arranged on the drive shaft, and that can be switched between the direction in which the first shaft and the second shaft are rotated and the direction in which the second shaft is rotated. The forward-reverse switching mechanism for the boat propulsion unit according to WO 2007/007707 A1 described above is constituted with two wet-type multi-plate clutch driven by hydraulic pressure and a planetary gear mechanism. The forward-reverse switching mechanism is constructed in a manner that the first shaft is rotated in a first direction and the second shaft is rotated in a second direction when the boat travels forward, and that the first shaft is rotated in the second direction and the second shaft is rotated in the first direction when the boat travels in reverse.
However, in the boat propulsion device (boat propulsion unit) disclosed in WO 2007/007707 A1, in addition to the two wet-type multi-plate clutch, the planetary gear mechanism is arranged in the forward-reverse switching mechanism arranged on the drive shaft. Thus, there is a problem in that the structure near the drive shaft is complicated and increased in size.